Baekjoon 10845.큐 c++ [Silver IV]

#include <iostream>
#include <queue>
#include <string>
using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int N;
    cin >> N;
    queue<int> q;

    while (N--)
    {
        string command;
        cin >> command;

        if (command == "push")
        {
            int x;
            cin >> x;
            q.push(x);
        }
        else if (command == "pop")
        {
            if (q.empty())
            {
                cout << -1 << "\n";
            }
            else
            {
                cout << q.front() << "\n";
                q.pop();
            }
        }
        else if (command == "size")
        {
            cout << q.size() << "\n";
        }
        else if (command == "empty")
        {
            cout << (q.empty() ? 1 : 0) << "\n";
        }
        else if (command == "front")
        {
            if (q.empty())
            {
                cout << -1 << "\n";
            }
            else
            {
                cout << q.front() << "\n";
            }
        }
        else if (command == "back")
        {
            if (q.empty())
            {
                cout << -1 << "\n";
            }
            else
            {
                cout << q.back() << "\n";
            }
        }
    }

    return 0;
}